1. Field of the Invention
The present invention relates to means for preventing reverse fluid flow through pipe. More specifically, the present invention relates to a check valve assembly suitable for employment in a drill string in which drilling fluid or "mud" is pumped downwardly through the string. The assembly is designed to prevent upward flow of the drilling fluid when the drill bit enters a high pressure area.
2. Description of the Prior Art
During the drilling of a well, there may arise a need for preventing the uncontrolled upward flow of drilling fluid or "mud" in the drill string, should the drill bit enter a high pressure area. Under normal operating conditions, unrestricted downward flow of the mud is desired. The prior art has suggested a number of check valve assemblies designed to allow fluids or fluent materials to be pumped downwardly through a drill string but to prevent reverse or upward flow therethrough. See, for example, U.S. Pat. Nos. 1,577,740 and 1,790,480.
If the valve elements of a check valve device are directly in the flow stream, the materials pumped through the drill string may erosively wear the valve components, particularly when such materials carry abrasive particles. Most check valve devices of the prior art employ a closure and seat assembly which is located directly in the flow stream and, therefore, subject to the erosive action of abrasive material in the fluid. Such valves, restrict the downward flow of fluid and, with the closure and seat assembly located directly in the flowstream, it is impossible for equipment to be lowered through the drill string past the assembly.
Furthermore, during drilling operations, the drill string must occasionally be removed from the well bore for maintenance of the drill bit. Any check valve device employed in the drill string should allow fluid to empty from the drill string as it is raised from the well bore. It is also preferable that the check valve device allow at least some reverse fluid flow through the drill string as it is being lowered into the well bore. This allows the drill string to be filled from the bottom so that fluid does not have to be pumped into the drill string from the surface to prevent collapsing because of pressure differentials. Valve assemblies of the prior art either allow no reverse fluid flow or a predetermined amount of reverse flow at all times. A valve that allows a predetermined amount of reverse flow at all times works fine when the drill string is lowered into the well bore; but, when the drill bit enters a high pressure area, it is impossible to completely stop flow.
Other devices, not designed for use in a drill string, have been developed to control only the upward flow of fluid in tubing. These devices are used in production strings to shut off the flow of oil or gas when damage occurs to equipment at the wellhead. See, for example, U.S. Pat. Nos. 3,269,463; 3,332,497; 3,332,498; 3,411,585; 3,568,768; 3,584,645; and 3,662,824.